1. Field of the Invention
The present invention relates to improvements in thermal regenerative desiccant apparatus and processes wherein desiccant elements move cyclically between process and regenerative gas streams. This invention involves separately heating each of a plurality of regeneration stream radial segments in a manner so that reduction from maximum thermal energy input is achieved by first reducing heat only in the first regeneration stream radial segment first contacting the desiccant element as it rotates from the process stream to the regeneration stream. When the heat supplied to the first regeneration stream segment has been completely discontinued, then for further reduction of heat, the heat supplied to only a second regeneration stream radial segment adjacent the first regeneration stream segment is reduced, and the reduction process continued sequentially across adjacent radial segments until desired total thermal energy input to the regeneration stream is achieved. The process of this invention for improved thermal desiccant regeneration is suitable for use in drying applications as well as in open cycle air conditioning apparatus and methods.
2. Description of the Prior Art
Thermally regenerated desiccant wheels are used in open cycle air conditioning systems as generally disclosed in U.S. Pat. No. 2,723,837, Neal A. Pennington and U.S. Pat. No. 2,926,502, C. G. Munters, et al. These desiccant wheels are regenerated by a regenerative air stream heated by means of an external heat source to a temperature sufficiently high to regenerate the hygroscopic material of the drying wheel passed in thermal exchange relation. U.S. Pat. No. 4,595,403 teaches regeneration of a desiccant wheel having ceramic fiber matrix with interstices filled with molecular sieves by heating the entire high temperature regeneration stream by burning gas in a heater.
U.S. Pat. No. 3,889,742, teaches staged heating which utilizes low level thermal energy from waste heat or solar sources applying heat to the entire regeneration stream and a high-temperature heater applying heat to the latter portion of the regeneration stream passing through the regeneration portion of the drying wheel of an open-cycle air conditioning system.
U.S. Pat. No. 4,729,774 discloses a method of regenerating desiccant beds or wheels by profiling the temperature of the regeneration air stream in a non-uniform manner over the surface area of the regeneration side of a desiccant component. The 4,729,774 patent teaches that the first portion of the regeneration stream seen by a revolving desiccant wheel is at a low temperature, the outlet temperature of the heat exchanger, and the heat may be increased in a staged manner or in a continuously increasing manner, so that the portion of the regeneration stream which the desiccant wheel sees last is at the highest temperature immediately prior to the desiccant wheel passing into the process air stream. The 4,729,774 patent teaches the desirability of the temperature profile of the regeneration side of the desiccant wheel corresponding to that of the process side. This is accomplished by means of direct thermal transfer from corresponding segments of the process stream side to the corresponding segments of the regeneration stream side which may be achieved through a stratified heat exchanger and baffle configurations in the regeneration stream. Any reduction in thermal input to the regeneration stream as taught by the 4,729,774 patent is effected across the entire regeneration stream.
U.S. Pat. No. 4,594,860 discloses an open cycle air-conditioning apparatus having a moisture transfer wheel and a heat exchanger wheel with baffles in the process stream between the moisture transfer wheel and the heat exchanger wheel to prevent undesirable mixing of process stream air at different temperature and humidity levels exiting from the desiccant wheel and passing to the heat exchange wheel.